Questions tagged [wilcoxon-mann-whitney-test]
The Wilcoxon rank sum test, also known as Mann-Whitney U test, is a non-parametric rank test to assess whether one of two samples has larger values than the other.
281
questions with no upvoted or accepted answers
18
votes
0
answers
691
views
Is the Wilcoxon two-sample test maximally powered to detect proportional odds alternatives?
We know from the literature that
The Wilcoxon-Mann-Whitney two-sample rank sum test is optimal for detecting simple location shifts when comparing two continuous random variables that each have a ...
- 83.7k
6
votes
0
answers
852
views
Power calculations for Wilcoxon test
I am running a Wilcoxon test to compare means between two groups (control and experiment) of unequal sample sizes. The distribution is right skewed and bound by zero for both groups.
I would like to ...
5
votes
0
answers
652
views
What model contains Wilcoxon's rank sum test?
As Frank Harrel mentions in the answer to Logistic regression and Wilcoxon test,
Wilcoxon's rank sum test (aka Mann-Whithey test) is contained in the proportional odds logistic regression, which would ...
- 11.5k
5
votes
0
answers
1k
views
Hypothesis testing with non-iid observations
I have a dataset with observations which violate the independent and identically distributed (iid) assumption. The dataset is composed by a number of post-click conversion events (purchases on a ...
- 293
5
votes
0
answers
404
views
When to use a chi-squared test?
This is a very basic question however I do not have a statistical background and I am currently analysing some data for my dissertation.
I have constructed a survey about healthy lifestyles & ...
- 51
4
votes
2
answers
464
views
Is Mann Whitney U the right statistical test for this analysis?
I am studying the spatial interactions between coral at a specific reef. I have the abundances of each coral species at each site we studied. I also have already run statistical tests and basically ...
- 41
4
votes
0
answers
1k
views
How to do a stratified nonparametric test?
I'm trying to use the "coin" (conditional inference) package to perform a stratified nonparametric test for difference in distribution (for count data).
I tried a stratified Mann-Whitney-Wilcoxon ...
- 41
4
votes
0
answers
98
views
Comparison of two means when they are means of means?
I have two vectors "$A$" and "$B$". Each vector contains multiple mean values derived from observations. The two vectors are subsets of a sample that has been categorized into five vectors. All ...
- 41
4
votes
0
answers
400
views
Minimum sample for non parametric test?
Exactly how many sample to be minimum size for non parametric test?
Right now i have 3 data with really2 small sample size
1. 5 pairs for wilcoxon signed rank test (pretest and postest in 1 place)
2. ...
- 41
4
votes
0
answers
2k
views
Reporting Mann Whitney test rejecting the null hypothesis, but samples have equal medians
I'm using the Mann Whitney test to verify if two population samples are equal. If the p-value is less than alpha (in this case, 0.05) I reject the null hypothesis and use the median of each population ...
- 551
4
votes
0
answers
4k
views
Comparing ROC-curves
I would like to find if there is a significant difference between two ROC-curves. I've found the roc.test in the pROC package. However, I cannot seem to find any information on how this test is ...
- 5,026
3
votes
1
answer
277
views
Comparison of different statistical tests on different amount of biological replicates
I am testing differentially expressed genes using different statistical tests on different amount of biological replicates (Wilcoxon test, t-test and negative binomial test). Figure below is what I ...
- 849
3
votes
0
answers
429
views
Multiple comparisons between two groups (non-parametric)
Update Added more details about the Experimental setup.
My experiment comprised two groups, control (N=25) and experimental (N=26). Each participant belonged to one group. Their performance has been ...
- 123
3
votes
0
answers
53
views
Algebraic Manipulations in Mann-Whitney-Wilcoxon Test Statistics
Given
Let $\Delta > 0 $ be positive real number. Consider the Wilcoxon-Mann-Whitney upper tail test $H_0: \Delta \leq 0 \,\,\, \text{vs} \,\,\, H_a: \Delta > 0$ aimed at testing the difference ...
- 165
3
votes
0
answers
344
views
Statistical method comparing difference in extreme percentile
Statistical methods like wilcox.test to t.test test differences in medians or means. I would like to compare the difference in ...
- 542
3
votes
0
answers
199
views
Can non-parametric tests, e.g. Mann-Whitney U, be used on non-normally distributed statistics off of bootstrap samples?
I have some return data from some different portfolios which I would like to compare using risk vs return ratios. The standard Sharpe ratio has a nice solution for calculating the significance of the ...
3
votes
0
answers
366
views
Combining paired and unpaired samples in Wilcoxon/MWU test
I am trying to compare numbers in two sets (X and Y) to test if numbers in one of the set are statistically larger than the others. However, some of the numbers are paired, and some are not. For ...
- 409
3
votes
0
answers
1k
views
Wilcoxon Rank-Sum vs Signed Rank for paired
I'm working with a dataset that contains paired samples (but some samples are missing their pair) and I want to check for an association between a binary variable and a bunch of numeric variables. ...
- 173
3
votes
0
answers
66
views
Manually computed Mann–Whitney U-test differs from R's output
I found a sketchy lecture notes about Mann–Whitney U-test. There where were given data
X: 30 32 33 33 36 37 40 44
Y: 27 29 31 34 34 35 41
It was computed that
...
- 31
3
votes
0
answers
170
views
List of sample arrangements at a given Wilcoxon / Mann-Whitney test statistic
Consider a Wilcoxon-Mann-Whitney test statistic, either in the form
(i) "W = sum of ranks in sample A"; or in the form
(ii) "sum of ranks in sample A - the minimum possible sum of ranks in sample ...
- 275k
3
votes
0
answers
4k
views
Different ways to calculate the test statistic for the Wilcoxon rank sum test
There are different ways to calculate the test statistic for the Wilcoxon rank sum test (quote from R help):
The literature is not unanimous about the definitions of the Wilcoxon
rank sum and ...
user14650
3
votes
0
answers
180
views
Semi-parametric approach: nonparametric test of residuals from linear mixed model
I want to know if this is a reasonable approach. I conducted the same experiment on two different species with small sample sizes (7-25 per species) in 4 years at 6 different sites. I measured damage ...
- 31
3
votes
0
answers
9k
views
Why does one get a 0.000 Mann-Whitney U value (not p-value) etc.?
1) Is it okay to run a Mann-Whitney U test on unequal sample sizes i.e. two groups (N=11, N=12)or is there an alternative test?
2) What does it mean when one obtains a zero value for a Mann-Whitney U ...
- 1,217
3
votes
1
answer
329
views
Most appropriate test for count data
So I've performed an experiment whereby I had 12 1km transects. 6 of these were along rivers running through agricultural land and 6 through woodland. These were arranged in pairs so that each agri ...
- 31
3
votes
1
answer
272
views
How to bootstrap for the standard error of a two sample test
I want to calculate the standard error of the area under the curve computed with the Mann-Whitney U-Test (MWUT).
Hanley and McNeil 1982 give a formula for it (they call the AUC calculated with the ...
- 464
2
votes
0
answers
30
views
When to use Spearman correlation and when to use Wilcoxon Rank sum test?
I have collected data on 1680 test scores and 1680 participation rates from 7 different courses and 4 different semesters using information from 60 students.
I am confused of whether to use a ...
- 21
2
votes
1
answer
73
views
Can I calculate ROC AUC from Mann Whitney U tests when I am comparing unequal sample sizes?
I know I am able to calculate Mann Whitney U tests when comparing 2 samples unequal inside but I am wondering if I am able to carry this same principle when calculating ROC AUC via the formula:
AUC = ...
- 21
2
votes
0
answers
136
views
How to conduct a boostrapped or a permutation wilcoxon test (in R)
I have a total of 18 mice, 9 from Healthy group and 9 from Sick group. Since I have a very poor sample size I would like to use boostrapping or permutation test.
Is there a way to conduct a ...
- 567
2
votes
0
answers
433
views
Mann-Whitney U Test test valid for percentages (% seagrass cover)?
Is the Mann-Whitney U Test test valid for percentages (not counts, but percent cover of seagrass)? All my data points are average percent cover of seagrass with about 53% of the data being zeros ...
- 1,041
2
votes
0
answers
31
views
How can I explain signifcant combined groups in Mann Whitney U but no individual effects in Kruskal Wallis?
I am struggling to get my head around the concepts of my tests and how to explain them. Unfortunately we didn't recieve much in depth teaching about it on my course.
I have 4 variables, one is a ...
- 21
2
votes
1
answer
137
views
How do I determine whether there is a significant difference between two sets of price data?
I am conducting a study where I am collecting prices from two groups of funeral homes in a particular state: in the first group, the homes I collected prices from are owned by families, and in the ...
- 21
2
votes
0
answers
1k
views
Actual difference between the statistic results from scipy.stats.ranksums and scipy.stats.mannwhitneyu
So, I have been trying to test if two independent samples come from the distribution, i.e. if they are greater or less than one another. Eventually I found out the Mann Whitney U Test is the ...
2
votes
0
answers
29
views
Testing tuples of response variables
I'm struggling with comparing samples with multiple response variables, where such variables have a strict precedence or importance order. For the sake of this exercise, let's assume that each sample ...
- 121
2
votes
0
answers
273
views
Estimating distribution of tied ranks for tie correction to Wilcoxon-Mann-Whitney U test
Tests based on ranking elements, such as
Mann, H. B.; Whitney, D. R. On a Test of Whether one of Two Random Variables is Stochastically Larger than the Other. Ann. Math. Statist. 18(1):50-60, 1947, ...
- 151
2
votes
0
answers
19
views
Non-parametric test for station variation
Certain disease reduces the concentration of calcium in people's blood. To test the effectiveness of a drug for the treatment of the disease, 9 individuals with the disease underwent an assessment in ...
- 562
2
votes
0
answers
34
views
One-sample versions of the signed rank and rank sum tests?
I wonder if there are applications of the signed rank and rank sum tests in a one-sample context?
Signed rank
Is there a form of the signed rank test where the difference $A-B$ for each subject is ...
- 28.9k
2
votes
0
answers
156
views
Test for different median in two independent groups with repeated measurements
I want to test if the median of a continuous variable (e.g. height) is the same in two independent groups (boys and girls). For each person there are multiple measurements of the continuous variable ...
- 311
2
votes
0
answers
263
views
If Mann-Whitney U is a median test? Then what the heck is "unpaired pairwise median"?
Header: I am really sorry for the confusing title. I am going to edit it so it fits the responses I get based on Mann Whitney U.
So I had this exact question on stack overflow about is the Mann ...
- 281
2
votes
0
answers
187
views
Testing differences in 5 star rating (Which hotel to choose)
Say, I want to choose a Hotel with the following ratings (1-5) on TripAdvisor.
This seemed interesting if the mean for the Hotel with smaller number of votes is bigger than the mean of the hotel with ...
- 83
2
votes
2
answers
201
views
Go with t-test or Mann-Whitney U test?
I'm measuring performance of 2 methods (method_A and method_B) that try to satisfy customers demands. Both methods produce ...
- 21
2
votes
0
answers
94
views
Whitney-Mann and multiple regression
Is it appropriate to use Whitney-Mann (to compare the groups) and multiple Regression model (to analyse each factor) within the same data? (parametric and non-parametric test on the same data)
- 21
2
votes
0
answers
462
views
Wilcoxon Test with Random Effect
I would like to test if there is a significant difference in the speed of movement between 2 treatments for different females. For each female, I have several sampling points. I have a table with the ...
- 21
2
votes
0
answers
171
views
multi-level Wilcoxon analysis
The question was originated from the paper [1] Table 3 [2], for every species, there was a data frame with two column: disease categories and the conservation index. Conservation index is numeric. The ...
- 269
2
votes
0
answers
506
views
Sample size for multiple hypothesis test: Wilcoxon test and Benjamini–Hochberg procedure
I have an experiment with a control and multiple treatments and want to find which one performs the best. I would use the Wilcoxon pairwise test to test all the hypotheses and correct the p-values ...
- 133
2
votes
0
answers
411
views
Adjusting P-Values of one-tailed tests
I am running a large number of two-sample Wilcox tests and using Benjamini, Hochberg, and Yekutieli method to adjust the p-values.
The issue is that when I conduct a one-tailed test, the p-values ...
- 21
2
votes
0
answers
280
views
T- tests on non-normal data
I keep reading mixed things about doing t-tests on non-normal data when the sample sizes are large and I don't know what to believe.
I have large samples sizes, over 1000 but the distribution is by ...
2
votes
0
answers
57
views
Groups with very unequal sizes
I want to compare means of the data of two human populations, group A has 12,400 (91.7%) subjects and group B has 1118 (8.3%). These are further subdivided to groups A1 (7598, 93.8%), B1 (499, 6.4%), ...
- 21
2
votes
0
answers
983
views
Mann Whitney U test or Kruskall-Wallis + Dunn test as a post hoc?
I performed a set of inhibition experiments where Lactobacilli supernatants where tested against a pathogen cell culture. These experiments were carried out in a 96-well plate where pathogen was ...
- 25
2
votes
0
answers
673
views
Confidence interval for Mann-Whitney test (Hodges–Lehmann estimator)
Does anybody knows how to calculate the confidence interval using normal approximation for the Hodges-Lehmann estimator (median of Y-X)?
This is how Minitab performs calculation, but I cannot find ...
- 581
2
votes
0
answers
98
views
Which Two-Sample Test for Non-Independent Data?
I am interested in determining whether there are statistically significant differences in the mean twelve-month (percentage) changes of various financial variables, conditioned on the state of the ...
- 21